Development and validation of alternative detection methods for performance indicators of the oxic state of bottom sediments



Impacts associated with uneaten fish feed and faeces - biochemical oxygen demanding (BOD) matter - from aquaculture activities are assessed by monitoring the oxic state, or oxygen concentrations, found within bottom sediments. Performance indicators such as sulfide concentrations and redox potential (Eh), which are commonly used to determine the impact of BOD matter deposits, have inherent limitations and discrepancies. These limitations have been attributed to variations in sampling, storage, and analytical procedures. This research project focused on developing and validating alternative detection methods of BOD matter impacts that are more robust while remaining practical for the industry. Alternative laboratory and field methodologies as well as technologies for measuring total free sulfides in sediment pore-water, was tested and adapted based on ultraviolet spectrophotometry and electrochemical (i.e., amperometric) micro-probes. New technologies for measuring dissolved oxygen (DO) concentrations were evaluated to determine their relevance and effectiveness in supporting management decisions based on the detection of BOD matter impacts. The intended outcome of this research project was to inform and enhance aquaculture regulatory monitoring programs, their results, and ensuing management decisions.


A broad suite of laboratory and field methods and technologies were tested for the analysis of dissolved oxygen and total "free" sulfide in sediment pore-water. Methodologies for the rapid field extraction of small aliquots of pore-water from sediment were tested that removed particulate contaminants and prevented exposure of samples to atmosphere, both of which would bias the classification of sediment oxic state. Several micro-sensors (Clarke-type and optical) proved to be adequate for monitoring dissolved oxygen. Initial development and adaptation of several methodologies was conducted to improve the reliability and practicality of total free sulfides measurements. Two methods were identified to be highly accurate (UV spectrophotometry and methylene blue colorometric analysis). The UV spectrophotometry method was shown to be simple and adaptable for conducting rapid measurements in the field. Laboratory analysis using the methylene blue microplate approach is more time consuming, but has potential for the bulk analysis of large numbers of preserved samples. This research improved both dissolved oxygen and total free sulfide methods, thereby improving accuracy of concentrations measured.



Program Name

Program for Aquaculture Regulatory Research (PARR)


2014 - 2015

Principal Investigator(s)

Peter Cranford
Research Scientist, Bedford Institute of Oceanography
1 Challenger Drive, Dartmouth, Nova Scotia

Team Member(s)

Blythe Chang

Fred Page

Terri Sutherland